The Maternal Health Practices and Child Development Project provides a unique opportunity to assess the development and maturation of young adults who have been followed since their fourth month of gestation through the age of 16. At this proposed phase, the offspring will be 21 years of age. We will explore the effects of prenatal marijuana exposure (PME) on the offspring in young adulthood. We will integrate this assessment with measures at prior phases and evaluate the developmental trajectories of these young adults across the multiple time points of the study. Importantly, at this proposed phase, we will assess the effects of prenatal exposure to marijuana on the transition into and adjustment to the roles and responsibilities of adulthood. The women in this project were interviewed in their fourth and seventh prenatal months and with their offspring at delivery, birth, 8 and 18 months, 3, 6, 10, 14 and 16 years of age. The cohort was selected from a prenatal clinic and the women represent the spectrum of prenatal marijuana use. At each of the 10 phases, we measured demographic status, the psychological, social, and household environment, maternal, paternal, and household substance use. We assessed the children's cognitive, behavioral, academic, psychological, physical, and neuropsychological status, and substance use and abuse. Study results to date demonstrate that marijuana exposure during gestation affects the development of the CNS, resulting in problems with mood, response suppression, and aspects of executive function. These outcomes, as well as the sequelae of these effects, such as academic difficulties and externalizing behaviors, may lead to more serious problems in adulthood. The deficits that result from prenatal exposure to marijuana have important implications for long-term development.